Several independent problems will be pursued under this grant. (1) Homogeneous histidine decarboxylase from Lactobacillus 30a contains covalently bound pyruvate and a functionally essential -SH group near the active center. Sequence studies are planned to determine the proximity of these two groups in the primary structure; if crystals of sufficient size can be obtained we will explore the possibilities of collaborative determination of the 3-dimensional structure of the enzyme. Histidine methyl ester inhibits irreversibly by covalent binding at the active site. If partial hydrolysis products can be obtained, further mapping of the active site will be possible. Histidine decarboxylase arises from an inactive proenzyme that lacks the pyruvate residue and contains only one species of peptide chain. Conversion of proenzyme to active enzyme involves chain cleavage and conversion of a serine residue to a pyruvate residue. Following rigorous purification of the proenzyme we will determine the effect of inhibitors, ionic strength, crude extracts, etc., on this conversion to determine its precise nature. (2) Mechanism and control of pantoate biosynthesis. We earlier discovered a folate-dependent synthesis of alpha-ketopantoate from HCHO and alpha-ketoisovalerate. The enzyme is of high molecular weight; we will purify if, determine its subunit structure and kinetic properties, and whether it is subject to feedback inhibition by pantothenate, or to some other type of control (most organisms do not excrete excess pantothenate). (3) We will study uptake of labelled vitamin B6 and pantothenic acid by organisms auxotrophic for these vitamins. These studies are closely related to vitamin B6 and is metabolic role, supported in this laboratory by a second USPH's grant.